iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev C1, Page 6/12
APPLICATIONS INFORMATION
Laser Power Adjustment
The iC-WJ and iC-WJZ devices can be adapted to CW
laser diodes from approximately 2 to 40 mW. N- and
M-type models can be used.
The pin ISET is used for the adjustment to the sensi-
tivity of the monitor diode and to set the desired optical
laser power. The setpoint for the averaging control of
the monitor diode current is preset at this pin.
3
REF
REFERENCE
DRIVER
1
VCC
5
+5 V
C1
100 uF
C3
4 ISET
THERMAL
SHUTDOWN
KLD
8
R1
12
Ω
6 IN
INPUT
VCC
REF
POWER DOWN
AMD
7
2 nF
LD
MD
RSET
74HCxx
2
4
WATCHDOG
1:1 iC−WJ
1:3 iC−WJZ
iC−WJ/WJZ
CWD
2
CI
470 nF
CI
3
GND
1
Figure 1: Operation of a laser diode according to the example
To calculate the current required at ISET, the average
optical laser power is to determine:
Example iC-WJ
Laser diode with 5 mW maximum optical output, mon-
itor diode with 0.13 mA/mW, pulse duty factor set to
20 % with
P
peak
= 5 mW:
The resulting average optical power is 1 mW and the
average monitor diode current is 0.13 mA. The resistor
RSET is calculated as:
P
av
=
P
peak
∗
t
whi
T
RSET
=
with peak value
P
peak
and pulse/period duration
twhi
twlo
Ppeak
CR1
∗
V
(ISET ) 1
∗
1.22
V
=
= 9.4
k
Ω
I
av
(AMD)
0.13
mA
with the Electrical Characteristics No. 301 for V(ISET)
and No. 108 for current ratio CR1.
Example iC-WJZ
Laser diode with 5 mW maximum optical output, mon-
itor diode with 0.75 mA at 3 mW, CW operation (pulse
duty factor 100 %) with
P
cw
= 1 mW:
t
whi
/T
.
T
Figure 2: Duty cycle
ICHAUS [ IC-HAUS GMBH ]
